Question

我有一个项目，我需要一个查询来使用表名来获取列的所有属性（列名，位置，数据类型，非空？和注释）。

我实现了获取列名，位置数据类型和非空？使用此查询：

SELECT column_name, data_type, ordinal_position, is_nullable 
FROM information_schema."columns"
WHERE "table_name"='TABLE-NAME'

但是，我需要评论！

Answer 1

这是针对system catalog的查询，该查询应该获取您需要的所有内容（免费提供奖励主键字段）。

SELECT DISTINCT
    a.attnum as num,
    a.attname as name,
    format_type(a.atttypid, a.atttypmod) as typ,
    a.attnotnull as notnull, 
    com.description as comment,
    coalesce(i.indisprimary,false) as primary_key,
    def.adsrc as default
FROM pg_attribute a 
JOIN pg_class pgc ON pgc.oid = a.attrelid
LEFT JOIN pg_index i ON 
    (pgc.oid = i.indrelid AND i.indkey[0] = a.attnum)
LEFT JOIN pg_description com on 
    (pgc.oid = com.objoid AND a.attnum = com.objsubid)
LEFT JOIN pg_attrdef def ON 
    (a.attrelid = def.adrelid AND a.attnum = def.adnum)
WHERE a.attnum > 0 AND pgc.oid = a.attrelid
AND pg_table_is_visible(pgc.oid)
AND NOT a.attisdropped
AND pgc.relname = 'TABLE_NAME'  -- Your table name here
ORDER BY a.attnum;

哪会返回如下结果：

 num |    name     |             typ             | notnull |       comment       | primary_key 
-----+-------------+-----------------------------+---------+---------------------+-------------
   1 | id          | integer                     | t       | a primary key thing | t
   2 | ref         | text                        | f       |                     | f
   3 | created     | timestamp without time zone | t       |                     | f
   4 | modified    | timestamp without time zone | t       |                     | f
   5 | name        | text                        | t       |                     | f

num：列号
name：列名
typ：数据类型
notnull：列是否定义为NOT NULL
评论：为列

COMMENT

primary_key：列是否定义为PRIMARY KEY
default：用于默认值的命令

Answer 2

建立在answer by @Chris：

之上

SELECT a.attnum
      ,a.attname                            AS name
      ,format_type(a.atttypid, a.atttypmod) AS typ
      ,a.attnotnull                         AS notnull
      ,coalesce(p.indisprimary, FALSE)      AS primary_key
      ,f.adsrc                              AS default_val
      ,d.description                        AS col_comment
FROM   pg_attribute    a 
LEFT   JOIN pg_index   p ON p.indrelid = a.attrelid AND a.attnum = ANY(p.indkey)
LEFT   JOIN pg_description d ON d.objoid  = a.attrelid AND d.objsubid = a.attnum
LEFT   JOIN pg_attrdef f ON f.adrelid = a.attrelid  AND f.adnum = a.attnum
WHERE  a.attnum > 0
AND    NOT a.attisdropped
AND    a.attrelid = 'schema.tbl'::regclass  -- table may be schema-qualified
ORDER  BY a.attnum;

可是：

表名在数据库中不唯一，因此也不在系统目录中。您可能需要对该名称进行架构限定使用a.attrelid = 'tbl'::regclass作为条件。这样您就可以传递myschema.mytbl作为名称并消除歧义。在这种情况下，根本不需要加入pg_class 此外，regclass会自动检查可见性，而不需要pg_table_is_visible()。

主键可以跨多个列。我通过pg_index加入a.attnum = ANY(p.indkey)来照顾这一点 indkey的类型为int2vecor，这是int2[]的特例，仅用于目录。

我发现psql -E对这类问题很有帮助。

兼容性

此类专用查询可能会在主要版本更新后中断。 Postgres不保证目录表保持稳定。基本元素变化的可能性极小，但查询越复杂和专业化，机会就越大。您可以使用information schema代替，这是标准化的，但也相对较慢。

Answer 3

我认为您可以使用：

select ordinal_position AS num, column_name as name, data_type as typ, character_maximum_length as lenth, 
is_nullable as nullable, column_default as default
from INFORMATION_SCHEMA.COLUMNS
WHERE table_catalog='DatabaseName' AND table_name='TableName'

如何使用PostgreSQL从表名中获取列属性？

3 个答案:

兼容性